DIY Router Guides, Collars and Templates With Fusion 360

With the right guide bush fitted to a router, an appropriate bit and a template/pattern, it’s easy to cut the shape you want accurately, and do it repeatably. The recesses for the inlays of the patterned plywood coasters in the photo were cut using the 3D-printed router guide and laser-cut pattern shown, and I've since made removable collars for my DIY guides that allow me to cut both inlays and pockets/recesses with the same pattern. This Instructable explains how it's done.

You can buy sets of guide bushes to fit the major brands of router, and some come with detachable collars. These commercially made guide bushes and collars are usually metal and probably last a lifetime, but they aren’t cheap (eg £40 for this brass set from Rutlands without collars, or £11 for a single, collarless bush from Toolstation) and I didn’t feel I could justify the cost just for the occasional job. Instead I 3D printed some guides and collars, then laser cut the patterns I needed, with everything designed in Fusion 360. Plastic guides and collars may not last as long as metal ones, but once you’ve designed them you can make as many as you need cheaply enough to replace them frequently.

Another advantage of using plastic guides is that you won’t damage the router’s collet if you make the mistake of plunging too deeply and driving the collet into the guide.

For this project you'll need to use:

• A router that will take a guide
• A straight bit suitable for plunge cutting (eg a spiral bit)
• Fusion 360 or another CAD system
• A 3D printer and filament (I used PETG)
• A laser cutter (or else make 3D-printed patterns)
• A chisel (not always needed)
• Double-sided sticky tape
• Wood glue
• Sandpaper
• A plane (not always needed)

And you'll also need these materials:

• Laser-safe 6mm / ¼” MDF, plywood or clear acrylic sheet
• A piece of wood to inlay
• Thin wood (say 3mm / ⅛" max) in a contrasting colour for the inlay

A router guide has a central bush (sometimes called a bushing or boss) that surrounds the router bit and is concentric with it. The bush projects below the router's baseplate - see 1st photo. The guide can be used to cut out a shape (either an inlay or the recess into which an inlay will go) by running the bush around the inside edge of a female pattern, so that the bit cuts a shape that’s smaller than the pattern. When making the recess, the material within the shape's outline needs to be removed too, of course.

As an alternative when cutting inlays, a male pattern can be used, in which case the guide bush runs around the outside edge of the pattern and the bit cuts a shape that’s bigger than the pattern. But such patterns can’t be used to create recesses – because the pattern is covering material that needs to be removed – which means you’d need a separate, female pattern to cut the corresponding recess. In this ‘Ible I’m concentrating on female patterns for that reason.

It’s vital for accuracy that the cutter is centred within the bush, we’ll deal with that in Step 6.

If you look at the two Fusion 360 screenshots above you’ll see that, for any given combination of pattern, guide bush diameter and bit diameter, the distance by which the outline of the cut is offset from the pattern is different for inlays and recesses. The first image shows an inlay being cut - the outer black line is the edge of the pattern, the dotted circles show the guide bush in 3 different positions as it's moved around the pattern, and the circles within represent the cutter. The inside edge of the cutter follows the purple line, except for the internal corners which become smooth curves. For an inlay, the offset is the distance from the outside of the bush to the further side of the cutter, its inside edge. Expressing this as an equation:

             offset_inlay = bush radius + cutter radius

Turning to the second screenshot, this shows the boundary of a recess (of the same size and shape as the inlay) being cut. This time, it's the position of the outer edge of the cutter that matters. If the same pattern is to be used, the guide bush - the dotted circles again - needs to have a larger diameter. For a recess, the offset is from the outside of the bush to the nearer side of the cutter. Or in equation form:

             offset_recess = bush radius – cutter radius

So how can you use the same pattern (and bit) to cut both an inlay and the recess it will fit into? By fitting a collar around the guide bush to increase its diameter when cutting the recess. Then,

             offset_inlay = offset_recess

which means:   

bush radius + cutter radius = bush radius – cutter radius + collar width

Therefore, collar width = 2 x cutter radius

In other words, the collar that’s fitted when cutting a recess must increase the guide bush radius by twice the cutter’s radius (or increase the guide bush diameter by twice the cutter’s diameter – it’s the same thing).

Maybe you’ve never thought about using a guide before and haven’t a clue whether your router can take one. Dig out the handbook and have a look through the accessories that came with the router, you might already have a guide. (I found one in the box, but it has a very large diameter bush and the bush's sides aren’t even straight.) Failing that, just have a look at the router’s underside. You’ll probably find 2 or more screw holes somewhere near the centre, offset above the baseplate. They might well be the same holes that are used to attach the dust extraction pipe.

Measure the flat plate of the existing guide carefully if there is one, otherwise measure the space it needs to occupy, including the screw hole size and locations. Unless you already have the right machine screws in the router kit, try a few different sizes until you find what the thread size and hole depth is - apparently M5 is the most common size. You will need screws with recessed/countersunk heads. Check the depth of the recess into which the guide will sit too, because it will need to be slightly thinner than the recess to make sure it’s clear of the baseplate.

Measure the inside diameter of the extraction pipe as well, that will come in useful if you want to ensure good sawdust removal without having to leave a big gap between the guide bush and the bit.

Based on the measurements you’ve taken, draw up the basic shape you need the plate of the guide to be in order to fit the router, including the screw holes, in Fusion 360. Note that it’s best not to fill the whole of the gap in the router’s baseplate with the guide’s base if you can avoid it – see the shape I produced in the above screenshot which is waisted with a gap top and bottom, like the metal guide that came with the router shown in the previous step. The gaps mean that there should be enough airflow to remove sawdust efficiently. So create some gaps in your design, without making the base of the guide so skeletal that its strength is compromised.

It’s important that the screw holes are in exactly the right position relative to the centre point, otherwise the guide bush won’t be concentric with the bit. If there are two screw holes then they should be equidistant from the centre and in a straight line with it, such that the guide could be fitted onto the router either way around. Make the centre point coincident with the origin and use the Mirror tool to get both halves of the shape identical.

I’d recommend extruding this shape to create a body of the required depth (just less than the recess, 1mm less is plenty) before adding the central hole and the bush, just to check the design. But before you save the file for 3D printing, chamfer the screw holes to the full depth of the screw heads you’re planning to use, you don’t want the heads to protrude at all below the guide.

Go ahead and slice the STL / OBJ file with a low percentage infill to save filament – not that it will make a lot of difference for something that’s only a few mm thick. Then print it and check that it fits well on the router and that the screw heads don’t protrude below it. Make any tweaks necessary to the design in order to get the shape and screw hole positions exactly right and then test again.

The internal diameter (ID) of the bush you make depends largely on the diameter of the bit you want to use it with – there has to be clearance around the cutter. And the tightness of the curves you can achieve when routing will be determine by the bush’s outside diameter (OD). The ID and OD are related, because the wall thickness of the bush must be sufficient to provide the necessary strength when you are gently pushing the bush against a pattern, especially given the fact that the guide will be 3D printed with the bush uppermost, which means that it’s weakest in the XY direction.

Another factor is that, to use the same pattern and bit for both inlay and recess, the guide bush’s diameter will have to be increased when cutting a recess by adding a collar. So it’s a good idea to keep the guide bush as small as possible for most pattern shapes. (It’s not important for cutting circles, as long as they’re no smaller than the collar’s OD.)

So here are a few things to consider:

• What shapes will you cut? What’s the smallest radius you can live with anywhere around the perimeter of the pattern?
• What diameter bits do you have that are long enough to protrude beyond the bush (which will itself protrude below the base plate) and that are suitable for both plunge cutting and sideways cutting?
• The smaller the bit diameter, the smaller the ID and therefore OD of the boss can be, and the tighter the curves you can cut. Which means less work with a chisel afterwards if you want sharp external corners. But small bits are easily broken. If this is the first time you’ve played around with pattern routing, I wouldn’t go any smaller than a 6mm / ¼” cutter.
• Aim for at least 2mm clearance around the bit to allow space for the sawdust generated to be sucked away efficiently, or you could get a build-up of dust between the guide bush and the edge of the pattern which will ruin inlays. (But see below for a possible solution.)

The good thing about making your own guides is it’s easy, quick and cheap to change the bush size. So experiment. To start with, I suggest making a small bush to suit a 6mm / ¼” bit – assuming you have one of that size.

Back in your Fusion 360 sketch, add two concentric circles at the centre point, one 10mm diameter (bush ID) and another offset from it by 2mm, ie 14mm diameter (bush OD). This gives a 2mm wall thickness and a clearance of 2mm around a 6mm bit, rather less for a ¼” bit. (One supplier of guide bushes, Rutlands – see Intro - recommends a 3.5mm clearance, but I haven’t had any problems with less. I guess it depends on how good the extraction is.)

Extrude the profile between these 2 circles by 5mm, in the same direction as the screw hole chamfers, joining the extrusion to the existing guide body. (5mm depth suits a pattern thickness of 6mm.) Then extrude a cut using the smaller circle as the profile, to create a clear path through the centre of the boss.

Dust removal can be a particular problem with smaller diameter guide bushes, because the area between the bit and the inside face of the bush is relatively small. Depending on whether you feel the gaps you created in the previous step (between the edge of the guide’s plate and the edge of the recess into which it will fit on the underside of the router) are sufficiently large, you may wish to draw a few small circles between the bush and the outer edge of the plate and then extrude them to cut ventilation holes. Ideally, keep them within the perimeter of the extraction pipe.

Finally, give the bush and the guide’s top and bottom surfaces a small fillet, say 0.25mm.

That’s all there is to it, so save the file and slice it. I print my guides in PETG with 30% infill and they work fine. You will need to achieve good layer adhesion though, which can be an issue with PETG but is usually resolved by slowing the print speed and reducing the fan speed or even turning the fan off. Let the bed and the print cool down fully before removing it, otherwise it may warp/bend and it’s important that the base that will be screwed onto the router is completely flat.

A removable collar is especially useful in that it enables one pattern to be used for both inlay and recess. (Remember, the collar’s width has to be the same measurement as the cutter’s diameter.) An appropriately sized collar also makes it possible to use two bits of different sizes while still cutting shapes of the same dimensions. But for a one-off inlay job, you might feel it’s too much of a fiddle getting the right collar clearance - see below – in which case you can simply print a second guide with a larger bush for cutting the recess.

For a collar, start a new sketch in Fusion 360 and project the outer edge of the bush into it from the previous sketch. You should have a 14mm diameter circle. Offset it by the diameter of the cutter, to give a circle of 26mm diameter for a 6mm bit. Then extrude the profile between the two circles to the same height as the guide bush to create a collar body.

Fillet the top and bottom faces by 0.25mm again, just to help with getting the collar onto the bush. As an added refinement to make it easier to remove, I created a small recess in the curved face on each side, near one end - see the first screenshot above. I make sure that’s the end that is pushed onto the bush then, if the collar should get stuck, I can insert a small screwdriver blade into the little gap to lever it off.

The final step is to create some clearance between the inside face of the collar and the outer face of the bush by using the push/pull tool to push back that face. You want the collar to slide on and off the bush without too much force, but once on stay put without being in any danger of falling off. Once it’s on it should be possible to rotate it with a little effort, but it definitely shouldn’t feel loose.

To work out how much clearance was needed, I saved several versions of my collar body as STL files, each with a different amount of “push”, and printed them all – they’re really quick prints, 15 minutes or less, just don’t get them muddled up. After trying the collars on the guide bush and finding the one with the face offset by 0.05mm (ie diameter 14.1mm) fitted best, I went back into my sketch and drew another circle, this one offset from the 14mm one by 0.05mm, and edited the extrusion to use that circle as the inner edge of the annulus. Finally, I deleted the last “push” from the timeline before saving. To me, this is neater than leaving the sketch as was and resetting the “push” distance to the right amount before saving. Either way, you now have a saved design you can amend easily to give you guides and collars to suit your needs, just by changing a few parameters. (You’ll find Change Parameters under the Modify drop-down. Go in there and label things like guide boss OD, collar OD and collar clearance in the Comments column, while you remember what’s what.)

The guide bush must be absolutely concentric with the router’s collet and the shaft of the bit, otherwise the offset will vary as you go around the edge of the pattern and the inlay won’t fit perfectly within the recess. It may be that this isn’t an issue with your particular router, because of the way the screws hold the guide in place. So perhaps miss out this step for now and see what results you get when you try inlaying a test piece and only come back here if the fit isn’t as good as you’d hoped.

A simple way of getting the guide’s alignment correct is to 3D print a cone that can be slid onto the shaft of a bit, pointing downwards towards the guide bush. The axis of the cone is aligned with the shaft. As a result, when the router is plunged far enough for the cone to engage with the circular hole in the centre of the bush, it will force the guide to move – provided the holding screws haven’t been fully tightened – to the central position. Then the screws can be tightened to keep it there. 

Bear in mind that you don’t need to use the same bit for this centring job as the one you’ll use for cutting. Choose one with as long a shaft as possible, but the cutter must be small enough to fit through the guide bush. Measure the shaft diameter accurately, I’ve found that the (nominal) ¼” bits I use measure closer to 6.40mm than 6.35mm.

To make a cone, create a new Fusion 360 sketch and draw a circle the same diameter as the shaft of your bit. Then draw a concentric circle of diameter a little greater than the largest bush internal diameter you ever expect to need, say 30mm. Create a conical body by extruding the profile of the large circle (all of it, including the small circle within it) at a 45° angle, as far as is necessary to bring the extrusion to a point. Then extrude the small circle through it, cutting a cylindrical hole all the way down the centre.

As when making the collar, the inner, cylindrical face of the cone needs a small offset to enable it to fit on a shaft. I pushed the face out by 0.05mm again, to give a diameter 0.1mm larger than the shaft, and that worked. You may need to try several versions before you get the right fit. It should be possible, but quite hard, to get the cone on and off.

To centre the guide bush, push the cone onto the shaft of a bit, with the small end of the cone towards the cutter and just clear of it. Then grip the shaft in the collet. Fit the guide bush in place but leave the screws loose enough to allow a little movement. With the router upside down, plunge it (gently!) to seat the guide bush’s opening on the cone. Holding it in place with one hand, tighten the screws with the other. Now you know that the guide bush is aligned with the collet and any other bit held in that collet. Remove the bit and slide the cone off its shaft.

Patterns can be cut using hand tools, but it’s quicker and almost certainly more accurate to laser cut them. It’s also perfectly feasible to 3D print them, but the prints will take a time and use a fair amount of filament because they need to be about 6mm / ¼” thick.

To design a pattern in Fusion 360, start by creating a sketch and drawing out the actual shape you want your inlay and recess to be. Maybe you already have in mind the shape you’d like, but if not then why not start with a bowtie, as is used to stabilise cracks in wood. A suitable size is 100mm wide with ends 45mm long and measuring 25mm across the centre. The Fusion 360 sketch screenshots in this step are for that size, using a 6.3mm diameter bit and a 14mm diameter boss.

Having drawn the outline of the shape you want to achieve, simply enlarge it using the Offset tool. The offset to use is (from Step 1) bush radius + cutter radius, in my case (14 + 6.3)/2 = 10.15mm. You can see from the left hand side of the second sketch screenshot that this will move the cutter around the inside of the desired bowtie shape to create the recess when a collar of 6.3mm width is added to give a total boss diameter of 14 + (2 x 6.3) = 26.6mm. The right hand side of the same sketch shows that the cutter will move around the outside of the shape to create the inlay when the collar is removed.

Sharp internal corners are impossible to achieve because the boss must pivot around them when cutting the inlay, but it won't be very noticeable unless the corners are acute or the bit has a large diameter. Also, the external corners of the recess will be rounded. You could radius them to match the bit, but it's not really necessary.

Draw a box around the shape of known size – this will be the outside edge of the pattern - leaving enough of a border to enable you to clamp the pattern down onto a workpiece, or at least glue it down temporarily. If you want to be able to align your inlays with each other or some other feature of whatever you are going to make, then make sure the inlay shape is perfectly aligned within the box and oriented correctly within in. You might want to add short perpendicular lines at the centre of each side of the box to help with placing it centrally on a marked spot. (These lines will instead need to be closed profiles that you can extrude for a 3D-printed pattern.)

Save your sketch and download it as a DXF file for laser cutting. For a 3D-printed pattern, extrude the pattern profile to 6mm thick and then recess the marks denoting the centre of each side below the surface, before saving the body as an STL for printing.

Strictly speaking, you should allow for the laser kerf when designing a pattern that’s to be laser cut, but it’s unlikely to be an issue given the accuracy that a router bit (and a 3D-printed guide) will achieve. In any case, both the inlay and the recess will be affected equally.

Now's the time to see if it works.

Take the pattern you made and clamp it down onto the wood into which you want to cut a recess. Fit the guide to the router and centre it as described in Step 6, then slip the collar onto the boss. (You're going to start by cutting the recess in order to get some practice at keeping the guide on the edge of the pattern before you cut the inlay.) After removing the centring cone and the bit that held it, fit the bit you're going to use - the one that suits the collar size.

Now place the router down on the wood with the guide boss within the pattern void. With the router turned off, plunge it gently until the bit touches the surface of the wood, and lock it at that depth. Set the depth guide to give you a cut depth of slightly less than the thickness of the inlay material, but no more than about 3-4mm. (If you want the inlay to be seated deeper than that, you'll need to cut the recess in two or more steps.)

Move the router to bring the guide boss into contact with the edge of the pattern. Then start it, plunge it to the required cut depth and lock it there. Move the router clockwise, keeping the guide in contact with the pattern at all times. When you've done a full circuit, stop the router, lift it clear and see how well you followed the outline. If you've drifted off into the body of the shape, be sure to practise more before attempting to cut the inlay, but it doesn't matter for the recess.

Now put the router back in place with cutter within the channel you've already created, start it again and clear out as much of the material within the outline as you can by moving the router back and forth and/or up and down in overlapping lines. If there are obstinate "islands" that you keep missing, remove them with a chisel instead.

Before cutting the matching inlay, remove the collar from the guide boss. You'll also need to stick down the underside of the material you'll be cutting with double-sided tape, in the correct zone, to a piece of scrap wood. You need scrap wood under the workpiece anyway because you'll be cutting right through it, and sticking down the inlay area means it won't come adrift and get damaged by the cutter once it's released from the rest of the material.

Set the depth to cut slightly deeper than the thickness of the inlay material. Then go ahead and cut the inlay, taking great care to keep to the edge of the pattern. It's a good idea to stop part way round and check that sawdust isn't accumulating - blow it away if it is - as it will take the cutter off course if it collects between the guide boss and the pattern edge. When you've gone all the way, separate the inlay carefully (especially if it's very thin) from the scrap wood by prising it off the tape with something like a palette knife or scraper.

The external corners of the recess will be rounded whereas the inlay's corners will be sharp. Either use the inlay as a template to draw sharp corners on the recess and then remove them with a chisel, or round the corners of the inlay with sandpaper.

Smooth the cut edges with sandpaper if necessary, then try the inlay in the recess. It should fit perfectly and be just slightly proud of the surface. Glue it into place if needed - it may be perfectly secure without if you need to tap it in quite hard with a mallet - and then sand it flush, or plane it if it protrudes too much for sanding. The final photo in this step shows a rather ugly looking plywood bowtie inlay which has had its outer layer planed off.